The search for processes to provide alternate feedstocks for fuels and chemicals, and particularly high quality diesel fuels and high value mixed linear alpha-alcohols, has been prompted due to the potential shortage of traditional petroleum reserves, and the increasing instability of international hydrocarbon resources.
Oil fields typically have deposits of natural gas associated with them. In remote locations where natural gas transportation may not be economically attractive, gas conversion technology can be used for chemically converting natural gas to higher molecular weight hydrocarbons. Current gas conversion technologies rely on the chemical conversion of natural gas to synthesis gas, which is a mixture of carbon monoxide and hydrogen. Synthesis gas is then reacted in a catalyzed hydrocarbon synthesis process commonly known as Fischer-Tropsch synthesis.
In 1923, Fischer-Tropsch synthesis process was provided, with the discovery of an efficient catalyst to convert synthesis gas into hydrocarbons mixtures. Coal-based synthetic fuels was produced during the World War II in Germany, and later in South Africa (SASOL), and the energy crisis of 70's and 80's renewed the interest toward the conversion of the increasing remote natural gas reserves to liquid fuel (GTL).
Alpha-alcohols containing 6 to 20 carbon atoms are useful as intermediates for the synthesis of plasticizers, detergents, lubricants and other surfactants. Therefore, processes for making mixed linear alpha-alcohols which comprises reacting a gaseous mixture of carbon monoxide and hydrogen in presence of an activated cobalt based catalyst are of commercial interest.
Generally speaking, mixed linear alpha-alcohols are often made through several steps, see for instance B. Elvers, et al., Ed., Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A28, 1996, p. 505-508 and references therein, and J. I. Kroschwitz, et al., Ed, Encyclopedia of Chemical Technology, 4th Ed., Vol. 1, John Wiley & Sons, New York, p. 894-903 and references therein, both of which are hereby incorporated herein by reference.
There are two processes for the production of synthetic linear alcohols which are (a) ALFOL® process and EPAL® process, based on the work of Prof. Dr. Ziegler using organic aluminum compounds and (b) the oxo-process (hydroformylation). The former process involves five steps: hydrogenation, ethylation, growth reaction, oxidation and hydrolysis, and the latter process consists of the reaction of olefins with a H2/CO gas mixture, in the presence of a suitable catalyst, wherein alpha-olefins yield approximately equal amounts of linear and branched aldehydes, and linear and branched alkenes can be used in this process due to double-bond being isomerized in the presence of the same catalyst. For a long time, paraffin-based process was predominant for the production olefins, especially used for detergents, now ethylene has became a preferable raw material. The principal steps in oxo-process are ethylene oligomerization, isomerization and metathesis.
Almost as old as the Fischer-Tropsch process for making hydrocarbons is the Fischer-Tropsch process for making alcohols. The Fischer-Tropsch process is carried out by passing a mixture of CO and H2 over a catalyst for the hydrogenation of carbon monoxide. Numerous catalysts and catalytic methods have been studied in attempt to provide a viable method for the production of aliphatic alcohols from synthesis gas.
Three main types of processes have been proposed for preparing alcohols from gaseous mixtures comprising carbon monoxide and hydrogen. One of these is a modified Fischer-Tropsch process which involves the use of alkali metal-containing iron based catalysts. Generally, this process suffers from poor selectivity and low productivity. Another process is the iso-butyl synthesis as used in Europe between 1935 and 1945. This process is analogous to the methanol synthesis process and utilizes a similar catalyst, i.e. zinc chromite, modified by addition of an alkali metal salt, at high temperature and high pressure. Typically, the main products from this process comprise methanol (50%), ethanol (20-40%), n-propanol and higher alcohols which are predominantly non-linear primary and secondary alcohols. The third process was originally assigned to Dow Chemical Company, in which primarily C1 to C4 mixed alcohols are produced in good yield over a supported catalyst based on molybdenum disulfide.
A typical review article related to alcohols preparation is R. B. Anderson et al. “Industrial and Engineering Chemistry” vol. 44, No. 10 pp. 2418-2424. A number of catalysts containing zinc, copper, chromium, manganese, thorium and iron, occasionally promoted with alkali or other materials for making various alcohols are listed in this article.
U.S. Pat. No. 4,504,600 provides a CO hydrogenation process for producing alcohols utilizing thallium-promoted iron-based catalysts. A mixture of CO and H2 is selectively converted to liquid C6˜C12 hydrocarbon containing C6˜C12 alcohols in an amount of 4˜8 wt. %, and methane in an amount of 1 wt. % relative to the total produced hydrocarbons, with a CO2 selectivity of 12˜18 mol. %.
U.S. Pat. No. 4,780,481 describes a process for manufacturing a mixture of saturated primary alcohols by reacting carbon monoxide with hydrogen in the presence of a catalyst formed essentially of copper, cobalt and zinc, promoted by alkali and alkaline earth metals and optionally zirconium and rare earth metals.
U.S. Pat. No. 4,725,626 discloses a catalyst and a process for the production of alcohols from CO and H2. The catalyst has the formula: RuCuaMbAcN2Ox, wherein A is an alkali metal or an alkaline earth metal or mixture thereof, and M is Mo or W or mixtures thereof.
U.S. Pat. No. 4,751,248 discloses a process for converting synthesis gas (H2/CO) to aliphatic alcohols containing at least 2 carbon atoms, comprising the steps of passing the synthesis gas first through a catalyst zone comprising wherein the catalyst comprises (a) Co metal and/or Co oxide and (b) MgO and/or ZnO (preferably MgO), and then through a catalyst zone wherein the catalyst comprises (c) Cu metal and/or Cu oxide and (d) ZnO.
U.S. Pat. No. 4,749,724 describes a process for forming an alcohol fraction boiling in the boiling range of motor gasoline that is enriched in higher alcohols, comprising the step of contacting containing a mixture of H2 and CO, and a lower alkanol with a catalyst comprising (1) molybdenum, tungsten or a mixture thereof in free or combined form; (2) an alkali or alkaline earth element; (3) a support.
EPO application 79-5,492 (Chemical Abstracts 92:166,257b), Hardman et al., discloses the production of alcohols using a 4-component catalyst, wherein the four components are copper, thorium, an alkali metal promoter, and a specific metal such as molybdenum. Chemical Abstracts 96:106,913x, Diffenbach et al., disclose a nitrided iron catalyst which is promoted by molybdenum for making alcohols from synthesis gas.
All of the aforementioned references are hereby incorporated herein by reference.
U.S. Pat. Nos. 4,675,344 and 4,775,696 state that a method for controlling the ratio of methanol and higher alcohols produced in a process for making mixed alcohols by contacting a H2/CO mixture with a catalyst which contains molybdenum, tungsten or rhenium, said method comprising adjusting the concentration of a sulfur releasing substance in the feedstock.
U.S. Pat. Nos. 4,752,623, 4,831,060 and 4,882,360 disclose a process for selectively making C1-C6 alcohols from synthesis gas, comprising the step of contacting a mixture of H2/CO with a catalytic amount of a catalyst wherein the catalyst is consisted of (1) a catalytically active metal, such as molybdenum, tungsten or rhenium; (2) a co-catalytic metal, such as cobalt, nickel, or iron; (3) an alkali or alkaline earth metal; (4) an optional support. The catalyst has to be sulfidized before the contact.
More recently, U.S. Pat. Nos. 6,248,796 and 6,753,353 disclose a method for the production of mixed alcohols by using a sulfidized transition metal catalyst selected from Group VI B metals, such as molybdenum or tungsten; nano-sizing the metal catalyst during its synthesis; suspending the catalyst in solvents to form a slurry; adding, a sulfur containing material to extend the catalyst life; and contacting this slurry with a mixture of CO and H2.
Previous catalytic methods have been notably effective for converting CO and H2 feedstocks into hydrocarbons and C1 to C6 alcohols, but none has been particularly effective for providing a substantial yield of a higher aliphatic C6 to C18 alcohols at a moderate temperature and pressure.
An extensive amount of works have been carried out in order to modify and improve the selectivity of a process for producing C6-C18 alcohols, especially C6-C18 linear alcohols, particularly under conditions that low methane and CO2 are produced. Such a process is desired since C6-C18 linear alcohols are industrially important and used in detergents, surfactants and plasticizers.
Thus far, no one has disclosed an activated carbon supported cobalt based catalyst which affords improved yields of mixed linear alpha-alkanols, naphtha distillates and diesel fuels from the reaction between carbon monoxide and hydrogen.
Naphtha is the most common feedstock sent to naphtha cracking units for the production of ethylene. A typical naphtha feedstock contains a mixture of paraffinic, naphthenic, and aromatic hydrocarbons with varied molecular weight and molecular structure. The compositions of naphtha feedstocks vary considerably, while the composition has a significant impact on ethylene and byproduct yields. Normal and branched paraffins convert to ethylene in a cracker, but the ethylene yield from n-paraffin is much greater than those from others. Naphtha is also used primarily as feedstocks for producing a gasoline component having high octane value via a catalytic reforming process. The naphtha distillates produced from Fischer-Tropsch process contains predominantly n-paraffins having 5 to 10 carbon atoms, which are excellent feedstocks for the production of ethylene.
Clean diesel fuels that contain no or almost no sulfur, nitrogen, or aromatics, are or will likely be demanded largely as diesel fuel or in blending diesel fuels. Clean diesel fuels with some mixed alcohols, having relatively high cetane number, are particularly valuable. Typical petroleum-derived distillates are not clean, in that they typically contain significant amounts of sulfur, nitrogen, and aromatics, and they have relatively low cetane numbers. Clean diesel fuels can be produced from petroleum-derived distillates through severe hydro-treating at great expense. The production of clean, high cetane number distillates from Fischer-Tropsch waxes has been discussed in the various literatures, but it is reported in few literatures that the catalyst can directly convert synthesis gas to diesel distillates with high quality or with some level mixed alcohols.
There is a need for a process by which mixed linear alpha-alkanols (C2-C18), naphtha distillates and diesel fuels with sulfur-free, nitrogen-free or aromatics-free can be directly synthesized from synthesis gas over an activated carbon supported cobalt based catalyst that cut off the heavier end of the Schultz-Flory distribution under moderate conditions.